A conventional adhesive material for electronic parts has been produced by the method as shown in FIG. 5, in which a base material 4 comprising a release sheet 41 having laminated thereon a double-side adhesive sheet 42 is passed under Thomson blade 5 whereby only the double-side adhesive sheet is cut to prescribed dimensions accurately corresponding to the shape of an adherent, and an unnecessary part 421 of the double-side adhesive sheet is removed from the release sheet 41 with double-side adhesive pieces 420 having a prescribed shape remaining on the release sheet with given spacings between them, which are then wound up together with a synthetic paper 6 for separation.
The thus produced adhesive material is used for adhesion in the manner shown in FIG. 6, in which an adhesive material A is continuously unwound at a constant speed, and double-side adhesive pieces 420 are transferred to adherends 7 that are forwarded at regular time intervals.
In the above-described adhesion system, a strict dimensional accuracy is required for the spacing between the double-side adhesive pieces. Any disorder in the prescribed spacing would result in failure to exacty adhere each of the double-side adhesive pieces to each adherend.
A polyethylene film is considered a promising candidate for a release sheet because of its good release property and dimensional stability against moisture. However, the polyethylene film has a small Young's modulus in tension so that a release sheet solely made of polyethylene is extended during cutting of the double-side adhesive sheet with a Thomson blade, readily resulting in disordered length of intervals between adhesive cut pieces.
U.S. Pat. No. 3,971,866 discloses a liner comprising a polyethylene film having formed thereon a reinforcing layer. This liner is composed of a thermoplastic resin layer having specific physical properties and a thermoplastic resin reinforcing layer having specific physical properties. The tensile load required for 10% elongation of this liner in tension at 325.degree. F. is about 3 psi/in or less. This liner is expected to be useful as a protective material for, for example, an ABS resin film having provided thereon an adhesive layer, and is exposed to heating such as vacuum molding together with the ABS resin. This is the reason for such a high elongation of the liner proposed in the aforesaid U.S. patent.
In order to eliminate the warpage of the release sheet due to elongation, it has been proposed to provide a silicone type release layer on one side of a polyester film.
However, since polyester has a great hardness, the impact applied during the cutting of the doulbe-side adhesive sheet with a Thomson blade is directly given to the interface between the polyester film and the silicone type release layer without being adsorbed, thus reducing the adhesion between the silicone type release layer and the polyester film. As a result, the double-side adhesive pieces tend to be accompanied with the silicone type release layer upon transferring to adherends so that it is impossible to adhere the surface of the double-side adhesive sheet pieces.